endymion summoning effect

the effect of endymion to recover a spell card from the graveyard is only when he is special summoned by his own effect removing 6 counters from the citadel?

Yes.

If he is normal summoned or summoned using other card effects then he won't be able to recover a spell card from the grave.

Yes, only when he summoned through his own eff (rmv 6 sp counter)

but he still can use the other effect?

The other effect doesn't related to the summon of Endymion so yes it can use.